Near-infrared spectroscopy (NIRS):
a) Measures saturation of arterial blood only
b) Relies on pulsatile flow for function
c) Correlates with slowing of EEG potentials at values 40% or more below
baseline
d) Cerebral and somatic values will both decrease in hyperventilated patients
e) Cerebral and somatic values will both decrease in anemic patients
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Answer
Answer e. NIRS measures saturation in both venous and arterial blood, and
represents an average blood and tissue saturation; it does not depend on
pulsatility for detection of arterial signal (as does pulse oximetry). Its somatic
and cerebral measurements are affected by changes in oxygen delivery and
consumption, and values more than 20% below baseline or less than an absolute
value of 40% are associated with slowing of EEG potentials and neurological
damage. A fall in cerebral compared to somatic rSO2 values may indicate
hyperventilation or a malpositioned aortic cannula, as hyperventilation will
decrease perfusion to the brain via cerebral vasoconstriction.
Notes
- This question originally printed in the Pediatric Anesthesiology Review Topics kindle book series, and appears courtesy of Naerthwyn Press, LLC.
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